Magnetic bearings realize super high speed rotation which is difficult to realize in ball bearings. Magnetic bearings used as machine tool spindles are also aimed at realizing super high speed rotation. Although the magnetic bearing realizes super high speed rotation, the magnetic bearing generates more heat than the ball bearing as the magnetic bearing has more electrical components than the ball bearing. Therefore, a cooing fluid is passed through a rotation shaft to cool the rotation shaft of a spindle unit. For example, Japanese Patent Application Laid-open No. H9-150345, discloses such a cooling apparatus.
This cooling apparatus suits well to a spindle unit that realizes a relatively low rotation speed, however, does not suit to a spindle unit that realizes a super high rotation range. Precisely, in the spindle unit that realizes a super high rotation range, mechanical parts that function as a path for the cooling fluid have limitations due to high speed performance, lifetime, and the like. Therefore, if this cooling apparatus used in the spindle unit that realizes a super high rotation range, these mechanical parts get damaged.
It is an object of the present invention to solve at least the problems in the conventional technology.
A magnetic bearing spindle according to one aspect of the present invention includes a rotation shaft that is held rotatably in a radial magnetic bearing rotor, an axial magnetic bearing rotor, a main shaft motor rotor, and an axial magnetic bearing stator, the axial magnetic bearing stator having an axial direction positioning member, an outer peripheral portion of the axial direction positioning member having a plurality of through holes, the outer peripheral portion of the axial magnetic bearing rotor is formed into a triangular shape or a shape corresponding to a triangular shape; a plurality of electromagnets disposed around the rotation shaft; and a casing that accommodates the rotation shaft and the electromagnets and includes an air passage to pass cooling air from outside to the through holes.
A magnetic bearing spindle according to another aspect of the present invention includes a rotation shaft that is held rotatably in a radial magnetic bearing rotor, an axial magnetic bearing rotor, a main shaft motor rotor, and an axial magnetic bearing stator, the axial magnetic bearing stator having an axial direction positioning member, an outer peripheral portion of the axial direction positioning member having a plurality of first through holes, portions of an outer magnetic pole tooth of the axial magnetic bearing stator, to which the axial magnetic bearing rotor is not opposed and which are not necessary for a magnetic circuit, are provided with a plurality of second through holes that are parallel to an axial direction of the rotation shaft and that communicate with the first through holes; a plurality of electromagnets disposed around the rotation shaft; and a casing that accommodates the rotation shaft and the electromagnets and includes an air passage to pass cooling air from outside to the first through holes.
A magnetic bearing spindle according to still another aspect of the present invention includes a rotation shaft that is held rotatably in a radial magnetic bearing rotor, an axial magnetic bearing rotor, a main shaft motor rotor, an axial magnetic bearing stator, and a main shaft motor stator, the axial magnetic bearing stator having an axial direction positioning member, an outer peripheral portion of the axial direction positioning member having a plurality of first through holes, a plurality of through holes that are parallel to an axial direction of the rotation shaft are provided in a portion of a core back of the radial magnetic bearing rotor and in a first portion of an outer magnetic pole tooth of the axial magnetic bearing stator and in a second portion of a core back of the main shaft motor stator that is disposed in the vicinity of the main shaft motor rotor, the first portion and the second portion being not necessary for a magnetic circuit; a plurality of electromagnets disposed around the rotation shaft; and a casing that accommodates the rotation shaft and the electromagnets and includes an air passage to pass cooling air from outside to the through holes.
The other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the present invention when read in conjunction with the accompanying drawings.